/*
** $Id: lstring.c $
** String table (keeps all strings handled by Lua)
** See Copyright Notice in lua.h
*/

#define lstring_c
#define LUA_CORE

#include "lprefix.h"


#include <string.h>

#include "lua.h"

#include "ldebug.h"
#include "ldo.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"


/*
** Maximum size for string table.
*/
#define MAXSTRTB cast_int(luaM_limitN(MAX_INT, TString*))


/*
** equality for long strings
*/
int luaS_eqlngstr (TString *a, TString *b) {
    size_t len = a->u.lnglen;
    lua_assert(a->tt == LUA_VLNGSTR && b->tt == LUA_VLNGSTR);
    return (a == b) ||  /* same instance or... */
           ((len == b->u.lnglen) &&  /* equal length and ... */
            (memcmp(getstr(a), getstr(b), len) == 0));  /* equal contents */
}


unsigned int luaS_hash (const char *str, size_t l, unsigned int seed) {
    unsigned int h = seed ^ cast_uint(l);
    for (; l > 0; l--)
        h ^= ((h<<5) + (h>>2) + cast_byte(str[l - 1]));
    return h;
}


unsigned int luaS_hashlongstr (TString *ts) {
    lua_assert(ts->tt == LUA_VLNGSTR);
    if (ts->extra == 0) {  /* no hash? */
        size_t len = ts->u.lnglen;
        ts->hash = luaS_hash(getstr(ts), len, ts->hash);
        ts->extra = 1;  /* now it has its hash */
    }
    return ts->hash;
}


static void tablerehash (TString **vect, int osize, int nsize) {
    int i;
    for (i = osize; i < nsize; i++)  /* clear new elements */
        vect[i] = NULL;
    for (i = 0; i < osize; i++) {  /* rehash old part of the array */
        TString *p = vect[i];
        vect[i] = NULL;
        while (p) {  /* for each string in the list */
            TString *hnext = p->u.hnext;  /* save next */
            unsigned int h = lmod(p->hash, nsize);  /* new position */
            p->u.hnext = vect[h];  /* chain it into array */
            vect[h] = p;
            p = hnext;
        }
    }
}


/*
** Resize the string table. If allocation fails, keep the current size.
** (This can degrade performance, but any non-zero size should work
** correctly.)
*/
void luaS_resize (lua_State *L, int nsize) {
    stringtable *tb = &G(L)->strt;
    int osize = tb->size;
    TString **newvect;
    if (nsize < osize)  /* shrinking table? */
        tablerehash(tb->hash, osize, nsize);  /* depopulate shrinking part */
    newvect = luaM_reallocvector(L, tb->hash, osize, nsize, TString*);
    if (unlikely(newvect == NULL)) {  /* reallocation failed? */
        if (nsize < osize)  /* was it shrinking table? */
            tablerehash(tb->hash, nsize, osize);  /* restore to original size */
        /* leave table as it was */
    }
    else {  /* allocation succeeded */
        tb->hash = newvect;
        tb->size = nsize;
        if (nsize > osize)
            tablerehash(newvect, osize, nsize);  /* rehash for new size */
    }
}


/*
** Clear API string cache. (Entries cannot be empty, so fill them with
** a non-collectable string.)
*/
void luaS_clearcache (global_State *g) {
    int i, j;
    for (i = 0; i < STRCACHE_N; i++)
        for (j = 0; j < STRCACHE_M; j++) {
            if (iswhite(g->strcache[i][j]))  /* will entry be collected? */
                g->strcache[i][j] = g->memerrmsg;  /* replace it with something fixed */
        }
}


/*
** Initialize the string table and the string cache
*/
void luaS_init (lua_State *L) {
    global_State *g = G(L);
    int i, j;
    stringtable *tb = &G(L)->strt;
    tb->hash = luaM_newvector(L, MINSTRTABSIZE, TString*);
    tablerehash(tb->hash, 0, MINSTRTABSIZE);  /* clear array */
    tb->size = MINSTRTABSIZE;
    /* pre-create memory-error message */
    g->memerrmsg = luaS_newliteral(L, MEMERRMSG);
    luaC_fix(L, obj2gco(g->memerrmsg));  /* it should never be collected */
    for (i = 0; i < STRCACHE_N; i++)  /* fill cache with valid strings */
        for (j = 0; j < STRCACHE_M; j++)
            g->strcache[i][j] = g->memerrmsg;
}



/*
** creates a new string object
*/
static TString *createstrobj (lua_State *L, size_t l, int tag, unsigned int h) {
    TString *ts;
    GCObject *o;
    size_t totalsize;  /* total size of TString object */
    totalsize = sizelstring(l);
    o = luaC_newobj(L, tag, totalsize);
    ts = gco2ts(o);
    ts->hash = h;
    ts->extra = 0;
    getstr(ts)[l] = '\0';  /* ending 0 */
    return ts;
}


TString *luaS_createlngstrobj (lua_State *L, size_t l) {
    TString *ts = createstrobj(L, l, LUA_VLNGSTR, G(L)->seed);
    ts->u.lnglen = l;
    return ts;
}


void luaS_remove (lua_State *L, TString *ts) {
    stringtable *tb = &G(L)->strt;
    TString **p = &tb->hash[lmod(ts->hash, tb->size)];
    while (*p != ts)  /* find previous element */
        p = &(*p)->u.hnext;
    *p = (*p)->u.hnext;  /* remove element from its list */
    tb->nuse--;
}


static void growstrtab (lua_State *L, stringtable *tb) {
    if (unlikely(tb->nuse == MAX_INT)) {  /* too many strings? */
        luaC_fullgc(L, 1);  /* try to free some... */
        if (tb->nuse == MAX_INT)  /* still too many? */
            luaM_error(L);  /* cannot even create a message... */
    }
    if (tb->size <= MAXSTRTB / 2)  /* can grow string table? */
        luaS_resize(L, tb->size * 2);
}


/*
** Checks whether short string exists and reuses it or creates a new one.
*/
static TString *internshrstr (lua_State *L, const char *str, size_t l) {
    TString *ts;
    global_State *g = G(L);
    stringtable *tb = &g->strt;
    unsigned int h = luaS_hash(str, l, g->seed);
    TString **list = &tb->hash[lmod(h, tb->size)];
    lua_assert(str != NULL);  /* otherwise 'memcmp'/'memcpy' are undefined */
    for (ts = *list; ts != NULL; ts = ts->u.hnext) {
        if (l == ts->shrlen && (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
            /* found! */
            if (isdead(g, ts))  /* dead (but not collected yet)? */
                changewhite(ts);  /* resurrect it */
            return ts;
        }
    }
    /* else must create a new string */
    if (tb->nuse >= tb->size) {  /* need to grow string table? */
        growstrtab(L, tb);
        list = &tb->hash[lmod(h, tb->size)];  /* rehash with new size */
    }
    ts = createstrobj(L, l, LUA_VSHRSTR, h);
    memcpy(getstr(ts), str, l * sizeof(char));
    ts->shrlen = cast_byte(l);
    ts->u.hnext = *list;
    *list = ts;
    tb->nuse++;
    return ts;
}


/*
** new string (with explicit length)
*/
TString *luaS_newlstr (lua_State *L, const char *str, size_t l) {
    if (l <= LUAI_MAXSHORTLEN)  /* short string? */
        return internshrstr(L, str, l);
    else {
        TString *ts;
        if (unlikely(l >= (MAX_SIZE - sizeof(TString))/sizeof(char)))
            luaM_toobig(L);
        ts = luaS_createlngstrobj(L, l);
        memcpy(getstr(ts), str, l * sizeof(char));
        return ts;
    }
}


/*
** Create or reuse a zero-terminated string, first checking in the
** cache (using the string address as a key). The cache can contain
** only zero-terminated strings, so it is safe to use 'strcmp' to
** check hits.
*/
TString *luaS_new (lua_State *L, const char *str) {
    unsigned int i = point2uint(str) % STRCACHE_N;  /* hash */
    int j;
    TString **p = G(L)->strcache[i];
    for (j = 0; j < STRCACHE_M; j++) {
        if (strcmp(str, getstr(p[j])) == 0)  /* hit? */
            return p[j];  /* that is it */
    }
    /* normal route */
    for (j = STRCACHE_M - 1; j > 0; j--)
        p[j] = p[j - 1];  /* move out last element */
    /* new element is first in the list */
    p[0] = luaS_newlstr(L, str, strlen(str));
    return p[0];
}


Udata *luaS_newudata (lua_State *L, size_t s, int nuvalue) {
    Udata *u;
    int i;
    GCObject *o;
    if (unlikely(s > MAX_SIZE - udatamemoffset(nuvalue)))
        luaM_toobig(L);
    o = luaC_newobj(L, LUA_VUSERDATA, sizeudata(nuvalue, s));
    u = gco2u(o);
    u->len = s;
    u->nuvalue = nuvalue;
    u->metatable = NULL;
    for (i = 0; i < nuvalue; i++)
        setnilvalue(&u->uv[i].uv);
    return u;
}

